It is known that oil and gas fields, rich in corrosive components, such as hydrogen sulfide, lie under the ground. In an oil well pipe including an oil pipeline/oil well tubular used to mine or transport oil and/or gas containing corrosive components (hereinafter referred to as “crude oil”) and a drill pipe for boring the ground while supplying mud slurry containing corrosive components, it is required that the inner surface of such a pipe, to which the aforementioned corrosive fluid continuously contacts while being renewed, has corrosion resistance against those corrosive components.
In view of this, it is preferable to use a high alloy pipe for the aforementioned oil well pipe. However, forming the entire thickness of the pipe by high alloy causes significantly increased cost, and therefore a clad pipe (double pipe), or a carbon steel pipe with an inner layer made of high alloy, has been normally used.
In conventional clad pipes, there are generally two types of structures. One such structure is disclosed, for instance, in JRCM NEWS/Vol. 166, published by Judicial Foundation of Material Research and Development Center, wherein a high Ni alloy with high corrosion resistance build-up is welded on an inner surface of a carbon steel pipe. One problem associated with this structure (i.e., build-up welding) is that since the build-up welding is performed on the inner surface of a long pipe, bending of the pipe occurs. Another problem is that, in the case of build-up welding, a diluted layer of the base material components and the build-up welding components is formed at the boundary portion between the base material of the steel pipe and the build-up welded layer. In order to form a build-up welding layer containing prescribed components with a predetermined thickness, it is necessary to further build-up a welding layer corresponding to the thickness of the diluted layer, which increases cost. Still another problem is that, due to the existence of the diluted layer, there is no clear boundary between the base material and the build-up welded layer. As a result, it is difficult to measure the wear status of the build-up welding layer from the outside of the pipe in a nondestructive manner. Another such structure is disclosed, for instance, in Japanese Unexamined Laid-open Patent Publication H06-142948, wherein a high Ni alloy pipe with high corrosion resistance is fitted in a carbon steel pipe and welded to the inner surface. With this structure, there must not be a gap between the inner pipe and the outer pipe when the inner pipe is inserted in the outer pipe to secure them. Because of this, it is required to strictly control processing tolerance of the inner and outer diameters thereof, which in turn increases manufacturing costs. Another problem with this structure is that it is difficult to manufacture a long article.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. Indeed, certain features of the invention may be capable of overcoming certain disadvantages, while still retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.